In order to overcome this problem, small-size winches which may be housed inside the travel shaft have been designed. These winches use brushless motors or conventional asynchronous motors complete with reduction unit, but, although they are able to eliminate the need for construction of a special machine room, they nevertheless have various drawbacks which are evident in particular in emergency situations.
Brushless motors use permanent magnets. When controlling the movement of the cage with the break released, i.e. when it is required to perform direct mechanical control of the winch operation, as occurs for example in emergency situations, the gradual demagnetisation of the magnets results in a loss of rapidity. Any mechanical blockage on the guides may be eliminated only by supplying a large quantity of power which, causing jerks and jolts, results in loss of continuity in mechanical control over the cage.
Moreover, visual control of the winch is not possible and, during the emergency manoeuvre, the operator must regulate releasing of the break based on his own sensation and impression gained from a direct view of the cables alone.
Positioning of the winch along the upper part of the guides also results in a less efficient sliding action of the said guides on the anchoring brackets, in particular when the cage must perform long travel movements, as well as deformation due to the excessive peak load.
Finally, the costs are higher than those of conventional asynchronous motors.
Asynchronous motors used in combination with a reduction unit, however, occupy a large amount of space due to the use of reduction units consisting of an endless screw/helical crown wheel pair, said units also having a low output and therefore requiring the use of high-power motors and therefore the consumption of a large quantity of electrical energy.
During the emergency manoeuvres, the reduction unit is situated in a position which is hidden from the operator and this means that the latter must control displacement of the cage solely by releasing the break and therefore in a somewhat unsafe manner.
Moreover, as in the case of brushless motors, positioning of the winch along the upper part of the guides diminishes the efficiency and reduces the reliability of the latter, resulting in deformation thereof due to the excessive peak load.